The present invention relates to a hydropneumatic suspension system for motor vehicles.
Hydropneumatic suspension systems are described, for example, in German Published Patent Application No. 195 21 747 and French Published Patent Application No. 2 761 008.
Hydropneumatic suspension systems offer decisive advantages in the areas of robustness, suspension comfort, as well as ease and speed of control. However, specific characteristics are a function to a great degree of the load state. A conventional hydropneumatic suspension system is composed of the fundamental elements, gas pressure reservoir, hydraulic cylinder, and connecting oil pressure lines. In place of the normal leaf, air, or coil springs, hydraulic cylinders are installed between the axle and the chassis. They are connected to gas pressure reservoirs by supply lines. The gas in each pressure reservoir acts as the spring, and the oil column in the supply line system acts as the medium transmitting the gas spring forces to the hydraulic cylinders. Damping occurs in the area of the oil column, using appropriate devices in the deflection and rebound directions.
German Published Patent Application No. 40 03 493 describes a hydropneumatic suspension system that has hydropneumatic support aggregates, that is assigned to the vehicle wheels, and an automatic level control system, that cooperates with the aggregates, the hydropneumatic suspension system sending hydraulic fluid, as a function of the lift position of the wheels, from a reservoir into the support aggregates, or drawing hydraulic fluid from the support aggregates into the reservoir.
To keep the power requirements of the system low, an active bypass and delivery system is arranged between the support organs, the bypass and delivery system, as a function of the lift position and/or of the pitch or roll torques acting on the vehicle, permitting the hydraulic fluid to shift between support aggregates arranged opposite each other with respect to the vehicle longitudinal axis and/or with respect to the vehicle transverse axis, circumventing the reservoir. In this hydropneumatic suspension system, the hydraulic fluid is therefore shifted directly between the support aggregates on different sides of the vehicle, or between the front and rear support aggregates, in order to elevate one vehicle side while simultaneously lowering the other vehicle side, or in order, correspondingly, to move the front of the vehicle in the opposite sense with respect to the rear of the vehicle.
German Published Patent Application No. 40 03 493 describes that the same cylinder spaces are supposed to realize both the functions of hydropneumatic suspension as well as roll stabilization. As a result, the hydropneumatic suspension has available to it not the entire piston surface, but rather only the surface on the piston rod side. Moreover, additional control elements are required for realizing the roll compensation.
It is an object of the present invention to provide a hydropneumatic suspension system which can perform the functions of suspension, roll stabilization, and automatic level control, without requiring supplemental control unit and control elements, and at the same time reducing the number of parts.
The above object of the present invention is achieved by providing a hydropneumatic suspension system as described herein.
By separating the suspension and roll-stabilizing cylinder spaces and at the same time by integrating the roll-stabilization control elements in the suspension cylinders, the component parts can be significantly reduced both in number and in weight. In addition, costly control technology can also be dispensed with.
A further advantage of the present invention is that by lowering the inner side of the vehicle, for the purpose of roll stabilization, the transverse acceleration is reduced, the center of gravity of the vehicle is lowered, and therefore the road holding capacity of the vehicle is improved.
The solution according to the present invention can be realized in at least four design variants. In a first example embodiment, the pressure supply lines of the suspension and automatic level control systems are separated, whereas in a second example embodiment, the systems are supplied by a central pump. The third and fourth example embodiments include a separate system for the front and rear axles, allowing the axles to be controlled independently of one another.